Authors: Paul R. Weissman & Harold F. Levison
Status: 1997. Astrophysical Journal Letters 488, L133-L136
Abstract: The unusual object 1996PW was discovered August 9, 1996 by the NEAT automated search camera operating from Haleakala in Hawaii. Although asteroidal in appearance, it was soon determined that the object is in a near-parabolic orbit similar to that of a long-period comet. No object which was not an active comet has ever been discovered on such an eccentric orbit. The discovery of 1996PW prompted us to examine and evaluate its possible origins, including the intriguing possibility that it is an asteroid from the Oort cloud. Current models for the formation of the Oort cloud argue that most of the material there should be from the Uranus-Neptune region and thus cometary, not asteroidal in composition. We better quantify these models and show that about 1% of the Oort cloud population should be asteroids. We find that 1996PW has almost certainly been a resident of the Oort cloud. However, we find it equally likely that 1996PW is an extinct comet or an asteroid. Though not conclusive, our results represent a significant change in our understanding of the Oort cloud, because they suggest that the ejection process sampled (1) material from as close to the Sun as the asteroid belt in the primordial solar nebula, and hence (2) much warmer formation temperatures than previously thought. This diverse sample is preserved in the Oort cloud.
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